dixie_boysles

[B]Written By: dixie_boysles


Discalimer: Neither I nor this site takes any responsibility in any damage or actions resulting from this . When performing this, you are doing so at your own risk

In this how-to I will be showing you my method to replacing the gear oil in your rear differential. There may be other ways, but this is the way that I found best. This was for my 04' Lariat with 3.73 Limit Slip.

Materials needed:

- 3 Qrts of 75W-140 Synthetic Gear Oil (I used Mobil 1) (your truck may call for different fluids)
- 1 Tube of TransX Friction Modifier (for people with limited slip only!!!)
- 1 tube of RTV Sealant
- 1 Can of brake cleaner
- Old Rags

Tools Needed:

- 3/8" Drive Ratchet
- 1/2" Socket
- Extension
- 1/2" wrench if needed
- razor blade or gasket scraper
- Hammer
- Oil Drain pan

Tips:

- Wear old cloths as you dont want gear oil or rtv sealant on you
- I wore medical gloves to keep the smelly gear oil off my hands (that stuff stinks)
- you should always loosen the fill plug before you start the job to make sure the plug will come out. You'll be in a tough situation if you pull the pan, drain the fluid, re-install the pan then find out you can't get the fill plug out.


Procedure:

Gather Materials:









Put truck in park and apply brake. Place Oil catch pan under rear differential





Using the 1/2" Ratchet or Wrench, start loosening all of the bolts

I took them all out but the top Two, used them to hold the cover so it wouldnt fall for the next step.





Once that is done, it's time to break the seal. Using a combination of the screw driver and the hammer, try to pry away the bottom of the cover from the axle. dont force too much in one area.

dixie_boysles

Then oil should start to drain



When it drain all the oil then go ahead and remove the remaining two top bolts.



Use the razor blade to clean both mating surfaces on the axle and cover





Use brake cleaner to clean the gears and the back of the diff cover





Once both surfaces are clean, apply RTV sealant around all the holes and a good solid bead around the perimeter of the cover



Put cover on and hand tighten all the bolts, let RTV dry for an hour then tighten completely using a cross bolt pattern similar to tightening lugs for wheels.

Using the 3/8" drive ratchet, loosen oil drain plug





Once loose, begin filling. I mixed my friction modifier with a qrt before putting it in. fill until the oil is level with the fill hole. Plug the hole. Done.

imac567

Great job on the picture tutorial! I have an old 91 f150, my manual says 5.5 pints but it took almost 6 for it to come out of the fill hole. Maybe I'm hearing things but it sounds different, almost like a light roar, is it possible to put too much in it?

bobkyle2

Moved and approved.

Lazarus-F150

Hey Dixie, thanks for the VERY well-documented post! I recently bought a 1992 F150 that needs some TLC (in addition to changing the rear differential fluid), so I am pretty new to these sorts of things. When you say "use brake cleaner to clean the gears" do you just spray it on and scrub the gears with a plastic-bristled brush (like a tooth brush?)? Any input would be greatly appreciated!

Thanks!

techrep

iTrader: (1)

I thought the Mobil 1 LS had friction mod in it already ??? If so why add a tube ??

Lazarus-F150

I have been looking around to try to figure out whether to use 75W-140 (as you did) or 75W-90. Alternatively, I have also seen several people use 80W-90 with added friction modifier for LSDs (when applicable). Can anyone explain why one would be better than the other? Looking at the Mobil1 info page, it sounds like the 80W-90 would be the closest match. I live in NC where winter temps are seldom below ~25F and summer can get ~100F.

Thanks!